Conjugated diene polymers are commonly used in the rubber industry. These polymers are often prepared by using coordination-catalysis techniques because the microstructure of the resulting polymer can be controlled. Polybutadiene having greater than 90 percent of its units in the 1,4-cis configuration can be produced with a coordination catalyst system that includes a nickel, cobalt, or titanium compound, an alkylating agent, and a halogen source. Polymers having this microstructure have a low glass transition temperature (Tg), which provides good low-temperature properties. Also, high 1,4-cis polymers have excellent wear resistance and mechanical properties such as reduced cut growth.
The tire industry has been challenged to design tires that have improved rolling resistance, which contributes to better fuel efficiency. Attempts to improve rolling resistance have included alternate tire designs and the use of rubber that has less hysteresis loss. Also, there has been a general trend toward the use of silica as a reinforcing filler. Polymers that interact with the fillers of tires have demonstrated less hysteresis loss.
Functionalized polymers prepared with anionic polymerization techniques have demonstrated lower hysteresis loss. They can be functionalized both at initiation and termination. Polybutadiene has been produced by initiating polymerization of 1,3-butadiene with functionalized initiators to provide polymers that have a greater affinity toward carbon black or silica fillers. Anionically polymerized polymers have also been terminated with functionalized terminators to provide polymers that have a greater affinity toward silica fillers. Unfortunately because anionic polymerization does not provide strict control over the polymer microstructure, high 1,4-cis polymers are not obtained.
Coordination catalysis limits the ability to functionalize the resulting polymers because they operate by chemical mechanisms that involve the interaction of several chemical constituents, and often also involve self-termination reactions. As a result, the reaction conditions required to achieve functionalization are difficult to obtain.
Terminating agents, such as organo metal halides, heterocumulene compounds, three-membered heterocyclic compounds, and certain other halogen containing compounds, will react with polymers prepared with a Lanthanide-based catalyst system. The resulting functionalized polymers, however, do not have a useful enough affinity toward either silica or carbon black fillers. And, in general they do not alleviate the cold flow problems associated with neodymium produced polymers.
Therefore, there is a need in the art to provide functionalizing agents that will react with polymers prepared with coordination catalysts to yield functionalized polymers having a high cis microstructure and an affinity toward silica.